L322 Range Rover System Description and Operation
INSTRUMENTS
88-10
DESCRIPTION AND OPERATION
The backlighting has manual and automatic brightness control. The manual brightness control is only available when
the lighting switch is on and is operated using the illumination dimmer rheostat on the fascia, adjacent to the lighting
switch. The automatic brightness adjustment is controlled by one of the instrument pack microprocessors and a
phototransistor. The phototransistor is located in the instrument pack, adjacent to the MIL/Service Engine Soon
warning lamp. The phototransistor measures the available ambient light and adjusts the display brightness
accordingly.
Odometer
The odometer displays the total distance which the vehicle has travelled. This is calculated by one of the
microprocessors using the wheel speed signals received from the ABS ECU. The total mileage information is made
available to other systems on the I and K Buses and is only transmitted in kilometres, irrespective of market
configuration.
The odometer display can show distances travelled up 999,999 miles or kilometres. When the ignition is off, pressing
the left hand instrument pack button, will allow the odometer reading to be displayed for 25 seconds.
The total distance is also recorded in the instrument pack EEPROM and RAM. This is recorded after every 2
kilometres travelled and transmitted to the LCM. This data is stored and compared to that of the instrument pack to
protect against illegal alteration of the odometer readings.
Trip meter
The trip meter displays the total distance which the vehicle has travelled since the last trip meter reset, up to 999.9
miles or kilometres. This is calculated by one of the microprocessors using the wheel speed signals from the ABS
ECU and is stored in the instrument pack RAM. The trip meter will restart at zero if the total distance exceeds 999.9
miles or kilometres.
The trip meter LCD also contains a small dot, known as the manipulation point. The manipulation point shows if there
is a total distance travelled or other data discrepancy between the instrument pack and LCM. Refer to 'Redundant
Data' section for further details.
Ambient Temperature
The external ambient air temperature is measured by a sensor located behind the Land Rover badge on the front grill
and is connected directly to the instrument pack.
The ambient temperature sensor is an NTC sensor whose resistance falls as the ambient temperature increases. The
instrument pack outputs a reference current of 5.1V to the sensor. The instrument pack microprocessor evaluates the
returned signal and converts the information into a temperature value and displays the appropriate temperature in the
LCD. The temperature display can be adjusted by TestBook/T4 to be displayed in either Celsius or Fahrenheit,
dependent on market requirements.
The instrument pack continuously transmits the ambient temperature signals on the CAN for use by other systems,
when the ignition is on. When the ignition is off, the instrument pack transmits an ambient temperature message on
the I/K bus, once every 10 minutes, for a duration of 400ms.
The sensor is capable of reading temperatures in the range of -45
°
C (-49
°
F) to +56
°
C (+132.8
°
F). The instrument
pack LCD will display minimum temperatures to -40
°
C (-40
°
F) and maximum temperatures to +50
°
C (+122
°
F).
The LCM monitors the temperature signals output on the bus systems. If the temperature falls to 3
°
C (37.4
°
F) or
below, the LCM outputs a message signal to instrument pack, when the ignition is on. The message signal is received
by the instrument pack which displays a message, 'EXTERNAL TEMPERATURE', with the recorded temperature
alongside. The instrument pack also emits a single chime from the sounder to alert the driver to the warning message.
The display time of the message is between 6 and 15 seconds, dependant on other displayed messages.
